It is common to employ biological indicators such as bacteria in sterilization processes to determine whether an article to be sterilized has been exposed to an efficacious level of the active ingredient(s) of the sterilant. Biological indicators may be used to provide assurance that sterilization conditions are met within the processor or processed load itself. Biological indicators may be used to represent the worst case for the processing system by providing an extremely large number of organisms highly resistant to that particular process within or upon the indicator. Spores are often used as the organism of choice for monitoring such sterilization processes. Typically, users of biological indicators rely on the visible effects which would follow the multiplication of any surviving viable organism to determine the efficacy of the sterilization process in which the biological indicators are employed. This process may take hours to days to produce a visible change such as turbidity in an incubation medium or color change in a pH indicator if such an indicator is used.
Biological indicators have been proposed that correlate the activity of an endogenous (internally derived, preexisting) thermostable enzyme present within a spore coat to the actual viability of the organism. This has resulted in biological read times ranging from minutes to hours with a fluorometer or colorimeter. Although these biological indicators provide a correlation between the activity of the enzyme and the viability of the organism, the actual results obtained are due entirely to the activity of the enzyme and have no direct linkage to the viability of the organism.
Biological indicators have also been proposed that correlate the activity of an exogenous (externally derived, not previously existing) enzyme that is produced upon chemical induction of a recombinant gene if there are viable test organisms present after the sterilizing event being evaluated bearing that gene. This gives biological read times ranging from minutes to hours with a fluorometric read and provides a direct linkage to the viability of the organism.